What is vaccine-derived poliovirus (VDPV)?

• A. It is poliovirus derived from attenuated Sabin strains in OPV that mutates to regain neurovirulence and transmissibility.
• B. It is a wild poliovirus unrelated to vaccines.
• C. It only occurs in animals.
• D. It is a lab-engineered strain used for vaccines.

Answer: (A)

Vaccine-derived poliovirus comes from the live, attenuated virus in the oral polio vaccine. Those Sabin strains are designed to provoke immunity by replicating in the gut, but occasionally the vaccine virus mutates as it passes through people. If it circulates in a population with incomplete immunity, it can gradually regain the ability to cause disease and to spread from person to person. When this happens, the virus is no longer just the vaccine strain but a diverged, neurovirulent, transmissible form—the vaccine-derived poliovirus. This is distinct from wild poliovirus and from lab-made strains, and it’s a key reason why high vaccination coverage and careful vaccine choices are important in polio eradication efforts.